The median age is the age that divides the population into two equal-size groups. Half of the population is older than the median age and half is younger. Median age is based on a standard distribution of the population by single years of age and is shown to the nearest tenth of a year. (See the sections on "Standard Distributions" and "Medians" under "Derived Measures.")

The data on marital status were derived from answers to Question 4. The marital status classification refers to the status at the time of interview. Data on marital status are tabulated only for people 15 years old and over.
All people were asked whether they were "now married," "widowed," "divorced," "separated," or "never married." Couples who live together (unmarried people, people in common-law marriages) were allowed to report the marital status they considered the most appropriate. When marital status was not reported, it was imputed according to the relationship to the householder and sex and age of the person.
Differences in the number of currently married males and females occur because there is no step in the weighting process to equalize the weighted estimates of husbands and wives.

Includes people whose current marriage has not ended through widowhood, divorce, or separation (regardless of previous marital history). The category may also include couples who live together or people in common-law marriages if they consider this category the most appropriate. In certain tabulations, currently married people are further classified as "spouse present" or "spouse absent."

Includes people legally separated or otherwise absent from their spouse because of marital discord. Those without a final divorce decree are classified as separated. This category also includes people who have been deserted or who have parted because they no longer want to live together but who have not obtained a divorce.

Includes people who are legally divorced and who have not remarried. Those without a final divorce decree are classified as separated. In selected tabulations, data for married and separated people are reorganized and combined with information on the presence of the spouse in the same household.

All people whose current marriage has not ended by widowhood or divorce. This category includes people defined above as "separated."

Spouse Present

Married people whose wife or husband was reported as a member of the same household or same group quarters facility, including those whose spouses may have been temporarily absent for such reasons as travel or hospitalization.

Spouse Absent

Married people whose wife or husband was not reported as a member of the same household or the same group quarters facility.

Separated

Defined above.

Spouse Absent, Other

Married people whose wife or husband was not reported as a member of the same household, excluding separated. Included is any person whose spouse was employed and living away from home or in an institution or serving away from home in the Armed Forces.
Differences between the number of currently married males and the number of currently married females occur because of reporting differences and because some husbands and wives have their usual residence in different areas. By definition, the numbers would be the same.

The median age at first marriage is calculated indirectly by estimating the proportion of young people who will marry during their lifetime, calculating one-half of this proportion, and determining the age (at the time of the survey) of people at this half-way mark by osculatory interpolation. It does not represent the actual median age of the population who married during the calendar year. It is shown to the nearest tenth of a year. Henry S. Shryock and Jacob S. Siegel outline the osculatory procedure in Methods and Materials of Demography , First Edition (May 1973), Volume 1, pages 291-296.

Beginning in 2007, people 15 years and over who were ever married (currently married, widowed, separated, or divorced) were asked if they had been married, widowed, or divorced in the past 12 months. They were asked how many times (once, two times, three or more times) they have been married, and the year of their last marriage.

Beginning in 2006, the population in group quarters (GQ) is included in the ACS. Some types of GQ populations have marital status distributions that are very different from the household population. The inclusion of the GQ population could therefore have a noticeable impact on the marital status distribution. This is particularly true for areas with a substantial GQ population.

The word "current" was dropped from the 1996-1998 question. Since 1999, the question states, "What is this persons marital status?" The American Community Survey began providing the median age at first marriage with the 2004 data.

People may have chosen to provide two or more races either by checking two or more race response check boxes, by providing multiple responses, or by some combination of check boxes and write-in responses. The race response categories shown on the questionnaire are collapsed into the five minimum races identified by the OMB, and the Census Bureau's "Some other race" category. For data product purposes, "Two or More Races" refers to combinations of two or more of the following race categories:
1. White
2. Black or African American
3. American Indian and Alaska Native
4. Asian
5. Native Hawaiian and Other Pacific Islander
6. Some other race

There are 57 possible combinations (see below) involving the race categories shown above. Thus, according to this approach, a response of "White" and "Asia"n was tallied as two or more races, while a response of Japanese and Chinese was not because "Japanese" and "Chinese" are both Asian responses. Tabulations of responses involving reporting of two or more races within the American Indian and Alaska Native, Asian, or Native Hawaiian and Other Pacific Islander categories are available in other data products.

White; Black or African American; Native Hawaiian and Other Pacific Islander; Some other race

White; American Indian and Alaska Native; Asian; Native Hawaiian and Other Pacific Islander

White; American Indian and Alaska Native; Asian; Some other race

White; American Indian and Alaska Native; Native Hawaiian and Other Pacific Islander; Some other race

White; Asian; Native Hawaiian and Other Pacific Islander; Some other race

Black or African American; American Indian and Alaska Native; Asian; Native Hawaiian and Other Pacific Islander

Black or African American; American Indian and Alaska Native; Asian; Some other race

Black or African American; American Indian and Alaska Native; Native Hawaiian and Other Pacific Islander; Some other race

Black or African American; Asian; Native Hawaiian and Other Pacific Islander; Some other race

American Indian and Alaska Native; Asian; Native Hawaiian and Other Pacific Islander; Some other race

White; Black or African American; American Indian and Alaska Native; Asian; Native Hawaiian and Other Pacific Islander

White; Black or African American; American Indian and Alaska Native; Asian; Some other race

White; Black or African American; American Indian and Alaska Native; Native Hawaiian and Other Pacific Islander; Some other race

White; Black or African American; Asian; Native Hawaiian and Other Pacific Islander; Some other race

White; American Indian and Alaska Native; Asian; Native Hawaiian and Other Pacific Islander; Some other race

Black or African American; American Indian and Alaska Native; Asian; Native Hawaiian and Other Pacific Islander; Some other race

White; Black or African American; American Indian and Alaska Native; Asian; Native Hawaiian and Other Pacific Islander; Some other race

Given the many possible ways of displaying data on two or more races, data products will provide varying levels of detail. The most common presentation shows a single line indicating "Two or more races." Some data products provide totals of all 57 possible race combinations, as well as subtotals of people reporting a specific number of races, such as people reporting two races, people reporting three races, and so on. In other presentations on race, data are shown for the total number of people who reported one of the six categories alone or in combination with one or more other race categories. For example, the category, "Asian alone or in combination with one or more other races" includes people who reported Asian alone and people who reported Asian in combination with White, Black or African American, Native Hawaiian and Other Pacific Islander, and/or Some other race. This number, therefore, represents the maximum number of people who reported as Asian in the question on race. When this data presentation is used, the individual race categories will add to more than the total population because people may be included in more than one category.